Zest citrus. Set aside.

Juice satsumas and lemon for 1/2 cup juice. Pour juice into a heavy-bottomed saucepan; turn heat to medium or medium-high. Bring juice to a simmer, whisking frequently, and cook until it has reduced to 1/4 cup, 5 – 8 minutes. Return heat to medium, whisk in butter and 3 tablespoons sugar, stirring until melted. Turn heat to low.

In a medium-sized bowl, beat egg. Whisking vigorously, add several tablespoons of hot citrus mixture. Continue adding a few tablespoons at a time until egg mixture has warmed. Whisking all the while, whisk egg mixture into warm citrus mixture. Adjust heat as needed to achieve a gentle bubble. Cook, whisking constantly, until mixture has thickened considerably and the whisk leaves trails in the curd, 3 - 5 minutes. If egg has cooked or clumped up at all, strain curd with a fine mesh sieve. Remove from heat, stir in reserved zest, and set aside.

Slice top and bottom from two satsumas. Using downward strokes, cut off peel. Slice peeled satsumas into 1/4-inch thick rounds.

Stir 1 teaspoon sugar into Greek yogurt.

Add a 2 tablespoon dollop of yogurt to the bottom of 4 1-cup glass jars. Next, add a tablespoon of curd. Continue layering, until all the yogurt has been used. Use a spoon to swirl layers – a single turn will do. Top with 2 satsuma rounds, cover, and chill 4 hours or overnight.